Description

At Sheridan College, psychology professor Peter Boyd helps science professor Hans Neumann by rescuing Bonzo, a baby chimp recently brought to America, from a suicide attempt. At the same time, ex-convict Breckenridge informs the college's dean, Tillinghast, that Peter's father was the legendary con man "Silky" Boyd. Tillinghast, who believes in the psychological theory that criminal tendencies are inherited, immediately presses Peter to resign and break off his engagement with Tillinghast's daughter Valerie, but Peter refuses. Instead, Peter returns to Neumann's laboratory, where he decides to bring Bonzo home and raise him as a human child, as part of an experiment that will prove that moral reasoning is learned not inherited.

After a long search for a "mother" for the chimp, Peter finally hires Jane Linden, a young governess whose maternal drive is matched only by her attraction to Peter. Over the next few weeks, Jane encourages Peter to act more lovingly toward Bonzo, and they set up a model home environment, in which Peter is called "papa" and Jane "mama." When Valerie grows suspicious of Peter's unavailability, he informs her of the experiment, but describes Jane as a matronly nanny. One afternoon, Bonzo acts morally for the first time when he returns Jane's necklace simply because she asks him to. Soon after, however, the mischievous chimp becomes frightened by the vacuum cleaner and escapes out the window into a tree. In an effort to retrieve him, Jane gets stuck in the tree while Bonzo climbs into the bedroom window and calls the police. After Peter gets stuck with Jane while trying to rescue her, the police arrive but refuse to believe that the chimp exists.

Valerie appears and hears the young, pretty Jane call Peter "papa," after which she throws his engagement ring at him. Back in the house, Peter wants to abandon the experiment since he no longer needs to prove to Tillinghast that environment matters more than genes, but Jane convinces him to carry on. Months later, as Peter prepares to address the Psychological Society with his findings that Bonzo can now reason morally, Tillinghast reveals to Hans that he has sold Bonzo to Yale's biomedical research facility. Before Hans can inform Peter, however, Jane overhears the psychologist say that he will fire her as soon as the research is done, and when she accuses Peter of having no heart and runs out, he finally realizes that she loves him.

That night, as Peter drives into town, Bonzo follows him but is distracted by a sparkly diamond necklace in the window of a jewelry store, which he then steals. Peter soon discovers Bonzo with the jewels, but is promptly arrested as he tries to return the necklace. Although Tillinghast and Valerie see this as proof of Peter's inherent lawlessness, Jane rushes to the police station to defend his innocence. After Jane insists that Bonzo stole the necklace and will prove his guilt by returning the jewelry to its rightful place, the police hide in the store to wait for Bonzo. At the last possible moment, the chimp climbs in through the heating vent and returns the necklace to its display, thus proving both Peter's innocence and his psychological theory that morality can be learned. Days later, Tillinghast beams with pride at the prestige that "Operation Bonzo" has brought to the college, while Valerie congratulates Peter on his marriage to Jane.